add new solutions

solutions/0/q77/solution.go

@@ -0,0 +1,51 @@
+package q77
+
+var (
+	allocBuf []int
+	allocP   int
+)
+
+func alloc(sz int) []int {
+	if allocBuf == nil || allocP+sz > 8192 {
+		allocP = 0
+		allocBuf = make([]int, 8192)
+	}
+	ret := allocBuf[allocP : allocP+sz]
+	allocP += sz
+	return ret
+}
+
+func combine(n int, k int) [][]int {
+	buf := alloc(k)
+	for i := range buf {
+		buf[i] = i + 1
+	}
+
+	sz := 1
+	for i := 1; i <= k; i++ {
+		sz = sz * (n - i + 1) / i
+	}
+	ret := make([][]int, 0, sz)
+	for {
+		t := alloc(k)
+		copy(t, buf)
+		ret = append(ret, t)
+
+		if buf[0] == n-k+1 {
+			break
+		}
+
+		buf[k-1]++
+		i := k - 1
+		for ; i > 0 && buf[i] > n-(k-1-i); i-- {
+			buf[i-1]++
+		}
+		for i++; i < k; i++ {
+			buf[i] = buf[i-1] + 1
+		}
+	}
+
+	return ret
+}
+
+var _ = combine